3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution), which is an advanced version of UMTS (Universal Mobile Telecommunications System) has been introduced as 3GPP release 8. 3GPP LTE adopts OFDMA (Orthogonal Frequency Division Multiple Access) for downlink and SC-FDMA (Single Carrier-Frequency Division Multiple Access) for uplink. MIMO (Multiple Input Multiple Output) having up to four antennas is employed. Recently, 3GPP LTE-A (LTE-Advanced) that is an evolution of 3GPP LTE has been intensively under discussion.
In HetNet, for high speed UEs, their handover failure rate is much higher than that for low speed UEs. In addition, for fast moving UEs, the potential offloading gain obtained from connecting to pico cells is very low because such UE has very short ToS. Therefore, it makes sense to prevent such UEs from performing handover into pico cells.
However, if the high speed UE cannot pass through the pico cell coverage before T310 expires, the UE will declare RLF. Then, the communication interruption time becomes longer because the UE should recovery connection with the serving cell after passing through the pico cell coverage.